Yes, there were players who splashed a second colour for utility and sideboard cards but before Sling-Gang Lieutenant goblins stuck to the consistency that a mono-coloured deck offered
If they don't, you may put a creature card with equal or lesser toughness from your hand onto the battlefield
For a blue mana, you can create a copy of this and target something else
You have to sacrifice those lands once theyve lost their counters, but access to a consistent proliferate source can keep them around forever, generating advantage every turn
Sealed examples with the original Pok Ball case fetch the highest prices
Costing just three mana, it is the one that you hard-cast the most often in fact, you will be hardcasting Endurance most of the time, and only pitching it when its very necessary to do so